Full color thick film dielectric electroluminescent displays, employing thin film phosphors and thick film dielectric layers, provide a greater luminance and superior reliability over traditional thin film electroluminescent displays. However, thick film dielectric electroluminescent displays employ phosphor materials and insulator materials that are susceptible to degradation due to reaction with water and other atmospheric vapors. Furthermore, the thick film dielectric layer of such displays, which enhances the luminosity of the displays to usable levels, may also be susceptible to degradation due to reaction with these atmospheric contaminants and may act as a reservoir for water and other contaminants that may react adversely with the display structure during operation of the display. Atmospheric contaminants are known to shorten the life of electroluminescent displays and thus in order to protect and minimize damage to these electroluminescent displays various types of seals have been developed for incorporation into displays.
U.S. Pat. No. 6,771,019 (the disclosure of which is incorporated herein in its entirety by reference) discloses the use of perimeter seals in thick film dielectric electroluminescent displays. Briefly, thin film phosphors are typically sandwiched between a pair of addressable electrodes and fabricated on a heat resistant substrate that is also impervious to water and atmospheric contaminants. The phosphor materials are activated by application of an electric field generated between the electrodes. A chemically impervious cover plate is typically placed over the fabricated display and sealed between the substrate and the cover plate with a perimeter seal in order to protect the phosphor material, dielectric layers and electrodes between the substrate and the cover plate. In some cases, the cover plate is on the viewing side of the display, in which case it must be optically transparent, and in other cases, the display is constructed on an optically transparent viewing-side substrate and the cover plate is positioned opposite the viewing side.
To further minimize ingress of atmospheric contaminants into the display structure a desiccant may be incorporated into the perimeter seal between the display substrate and the cover plate as exemplified by Applicant's co-pending International Patent Application serial number WO2004/067676 (the disclosure of which is incorporated herein in its entirety), however, the desiccant has a finite capacity to absorb these contaminants.
Sealing layers have also been developed for use with other types of displays. For example, U.S. Pat. No. 5,920,080 discloses an organic light emitting device (OLED) constructed on a substrate that has incorporated a top cover structure that includes an amorphous carbon or silicon carbide moisture barrier layer above the top conductor of the OLED and a further sealing layer comprising a heat sink gel material containing a particulate moisture getter such as barium oxide above the moisture barrier layer. There is also a cover glass over the display substrate and bonded to the substrate to form a perimeter seal around each display.
U.S. Pat. No. 6,146,225 discloses a barrier for preventing water or oxygen from reaching an organic light emitting device. The barrier comprises layers of polymer having an inorganic layer comprising oxides, oxy-nitrides or nitrides therebetween. A getter material can be provided in the inorganic layer or as a separate layer between the polymer layers and the display, but the getter has a finite capacity to absorb contaminants.
U.S. Pat. No. 6,891,330 discloses an organic electroluminescent device, the surface of which is coated with a multilayer barrier coating of an organic polymer and inorganic material.
U.S. Pat. No. 6,896,979 discloses a film for use in organic EL devices which is made of an organic inorganic hybrid material. The film is used as a gas-barrier to encapsulate the device.
While the aforementioned references may teach the use of various types of seals and seal arrangements for electroluminescent displays, these seals and seal arrangements may not adequately immobilize the flux of atmospheric contaminants into the electroluminescent displays over the intended life of the display. They may also not adequately address the water and other contaminants that may reservoir within the thick film dielectric layer that may react adversely with the display structure during operation of the display. Therefore, there still remains a need for a proper seal and sealing process for thick film dielectric electroluminescent displays in order to improve their operating stability.